In DSL technology, faults and issues in the physical wiring between the DSLAM (DSL Access Multiplexer) (which could be located in e.g. a Central office (CO) or in a street cabinet) and Customer premises equipment (CPE) cause today an unacceptable error rate for high demanding applications as video, audio streaming, and gaming (=triple play). A typical wiring issue can be a portion of unbalanced or untwisted pair, which causes susceptibility for radiation from external sources to be picked up, and disturbs the DSL signal. This external noise signal is typically received in common mode interference on the twisted pair, and translates into differential mode interference at locations where the line or cable is unbalanced or untwisted.
Such wiring issue often occurs at locations where twisted cable segments are connected to each other:                at Main Distribution Frame (MDF) at the Central Office where the DSLAM is located;        at MDF in the Remote Unit;        at any connection point in the street between the CO and houses of end-users where the Customer Premises Equipment (CPE) is located;        in the houses of end-users where wiring segments link the incoming twisted pair with the CPE.        
Some existing systems allow sensing the fact that a line suffers from a higher than expected amount of disturbing noise caused by an external source, but these systems cannot determine the location of the noise injection and thus of the defect. This makes repairing the line very difficult, as a DSL loop can be several kilometers long which makes it inefficient to check any possible connection point of a line. Often the line is not physically accessible for a technician over at least a part of its length.
There is a need for methods and systems which are capable of efficiently locating the defects in transmission lines.